Please refer to FIG. 11 and FIG. 12 respectively for a conventional T-slot cutter 80 and a conventional side milling cutter 90, both with soldered blades. These milling cutters 80, 90 are multi-point cutting tools designed mainly for forming T slots or other types of grooves. A traditional T-slot cutter or side milling cutter typically has soldered blades, which are soldered to the body of the cutter with copper as the soldering material. Such T-slot cutters and side milling cutters feature low rotation speeds, but their multiple cutting edges contribute to high chip removal rates. Nowadays, the most common blade materials are high-speed steel (HSS) and tungsten carbide (WC). HSS has a hardness of HRC 66˜68 and can withstand temperatures as high as 600° C. However, HSS blades tend to lower both processing speed and feed speed and therefore give way to WC blades when high processing speed is desired. WC cutters are harder and can tolerate higher temperatures than their HSS counterparts, and yet a milling cutter with soldered WC blades cannot be coated in a typical coating environment, whose temperature ranges from 300° C. to 800° C., for the copper used to solder the WC blades to the milling cutter will soften at about 300° C.˜400° C. This explains why milling cutters with soldered WC blades cannot be coated with titanium, and the lack of this titanium coating hinders further improvement of such milling cutters in hardness, wear resistance, and temperature resistance. Now that cutting speed and feed speed cannot be raised, effective enhancement in processing efficiency is unattainable.
In view of the fact that milling cutters with soldered blades have problem being coated with special metals (e.g., titanium), disposable T-slot cutters and side milling cutters are called for, whose uses are briefly stated as follows:
T-slot cutters: Conventional disposable T-slot cutters have an outer diameter of about 21˜50 mm. Referring to FIG. 13, the conventional disposable T-slot cutter 50 has an outer diameter D1 of 50 mm and four disposable blades 51, wherein each two adjacent disposable blades 51 (e.g., the disposable blades 51a and 51b) are positioned in a staggered arrangement (i.e., not aligned with each other), thus jointly forming an effective cutting edge with a cutting edge width W1 extending in an axial direction X1. In other words, each effective cutting edge of the disposable T-slot cutter 50 is defined by two adjacent disposable blades 51 (e.g., the disposable blades 51a and 51b). Hence, the number of the effective cutting edges of the disposable T-slot cutter 50 (i.e., two) is only half of the number of its disposable blades 51. By the same token, if a conventional disposable T-slot cutter with an outer diameter of 21 mm has two disposable blades, there will be only one effective cutting edge. In the case of a T-slot cutter with soldered blades, however, each blade forms an effective cutting edge (See FIG. 11). That is to say, a T-slot cutter with soldered blades has as many effective cutting edges as its blades.
According to the above, given the same number of blades, the number ZC of the effective cutting edges of a disposable T-slot cutter is only half of that of a T-slot cutter with soldered blades. Since the feed speed Vf of a milling machine is in direct proportion to the number Zc of effective cutting edges (Vf=fz×N×ZC, wherein Vf is feed speed of a milling machine, fz is feeding amount of each effective cutting edge, N is the number of revolutions of the main shaft per unit time, and ZC is the number of effective cutting edges), a disposable T-slot cutter does not provide a significant increase in cutting efficiency as compared with a T-slot cutter with soldered blades. Apart from that, given the same cutting conditions (e.g., high speed and heavy-duty cutting), the shaft of a disposable T-slot cutter is more likely to undergo noticeable deflection than the shaft of a T-slot cutter with soldered blades. The deflection not only impairs the precision of cutting but also shortens the service lives of the affected cutters.
Side milling cutters: Conventional three-face disposable side milling cutters have an outer diameter of about 100˜160 mm. Referring to FIG. 14, the conventional disposable side milling cutter 60 has an outer diameter D2 of 160 mm and ten disposable blades 61, wherein each two adjacent disposable blades 61 (e.g., the disposable blades 61a and 61b) are positioned in a staggered arrangement (i.e., not aligned with each other) and thus jointly form an effective cutting edge with a cutting edge width W2 extending in an axial direction X2. In other words, each effective cutting edge of the disposable side milling cutter 60 is defined by two adjacent disposable blades 61 (e.g., the disposable blades 61a and 61b). Therefore, the number of the effective cutting edges of the disposable side milling cutter 60 (i.e., five) is only half of the number of its disposable blades 61. By contrast, a side milling cutter with the same number of soldered blades has ten effective cutting edges. That is to say, the number of the effective cutting edges of a disposable side milling cutter is only half of that of a side milling cutter with the same number of soldered blades. Consequently, a disposable side milling cutter does not provide a significant increase in cutting efficiency as compared with a side milling cutter with soldered blades.
The main reason why the number of the effective cutting edges of a disposable T-slot cutter or disposable side milling cutter cannot be increased lies in the positioning structure of the disposable blades 51, 61. More specifically, referring to FIG. 14, each disposable blade 61 requires not only to be locked to a blade seat 62 of the disposable side milling cutter 60 by a screw 30, but also to be supported by the two perpendicularly connected sidewalls 621 and 622 of the blade seat 62 in order to resist great cutting stresses, which otherwise will be borne by the screw 30 alone. If, referring to FIG. 15, each disposable blade 61 is held in place by the locking force of the screw 30 and the supporting force of only one sidewall 621, the maximum cutting stress each disposable blade 61 can cope with will be lowered considerably. As each blade seat 62 of the conventional disposable side milling cutter 60 must have two sidewalls 621 and 622 connected at an angle of 90 degrees, the number of the effective cutting edges of the cutter is reduced. It is this conventional blade positioning design that keeps the cutting efficiency of disposable T-slot cutters and disposable side milling cutters from betterment.